1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a diffraction optical element such as a zone plate, binary optics, or the like.
2. Description of the Related Art
In recent years, a so-called diffraction optical element has received a lot of attention as an optical element used in a projection exposure apparatus or the like. The diffraction optical element deflects an optical path by utilizing a diffraction effect. The diffraction optical element can arbitrarily deflect the optical path of a light beam of a short wavelength, and exhibits wavelength-deflection characteristics different from those of a refraction lens. For this reason, an application such as a new aberration correction member upon combination with a refraction lens is expected.
As the diffraction optical element, a so-called zone plate is known. As the zone plate, a Fresnel zone plate which has a structure constituted by arranging concentric circular light-shielding members on a light-transmitting substrate, as shown in FIGS. 4A and 4B, is known. Also, a so-called binary optics (BOE) in which concentric circular regions with different transmission characteristics (refractive indices, transmission distances, and the like) are arranged stepwise (to have a staircase sectional shape) to locally vary the transmission distance of a light beam incident on the element, so as to obtain a diffraction effect, is proposed as a new zone plate.
Such an optical element is described in U.S. Pat. Nos. 5,156,943 and 4,895,790. Apparatuses described in these patents cannot manufacture a diffraction optical element with a precision pattern.